1. Technical Field of the Invention:
The present invention relates to the treatment of spent catalysts contaminated or poisoned with arsenic in order to regenerate them and render them suitable for reuse.
2. Description of the Prior Art:
The treatment of contaminated spent products is an activity which today is becoming increasingly important. Environmental restrictions are resulting in the purification of all types of liquid, solid or gas with the goal of diminishing their levels of pollutants and preventing discharge of same to the environment.
Many catalysts have been developed for the purpose of removing the aforesaid impurities by absorption, adsorption or chemical reactions. However, once the contaminated products have been purified, the impurities exist at high concentrations in the catalysts, which must then be stored or destroyed.
There currently is a tendency to treat these spent catalysts to remove the impurities therefrom. This treatment targets, on the one hand, recovering impurities, in order to profit therefrom or to convert them into a form which can be easily stored, and, on the other, regenerating the spent catalysts in order to reuse them. This second aspect, in addition, permits savings, since it is not necessary to repurchase another charge of fresh catalyst.
Arsenic plays an important role among the impurities which are particularly harmful to the environment. In particular, it is present in gases, such as cracked gases resulting from steam cracking. One means for removing arsenic from these gases is to contact same with a catalyst based on a lead compound, for example a supported catalyst having an active phase based on a lead compound, for example lead oxide.
The arsenic present in the gases reacts on contact with these catalysts to form an arsenic compound, in particular a mixed compound of lead and of arsenic, which remains ad/absorbed on the catalyst.
Spent catalysts comprising these arsenic compounds are presently destroyed or stored. In addition, a new charge of fresh catalyst must be employed in order to continue to treat the gases to be purified.